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1.
Because of the rapid increase in the number of snowboarders many kinds of snowboards have been developed recently. To design a snowboard or to improve its quality, the natural frequency of the snowboard seems to be one of the most important properties to be discussed. In this study whether or not one can accurately estimate the natural frequency of the snowboard by using the numerical approach proposed for a free vibration of an inhomogeneous plate is discussed. First, the convergency of the natural frequency is discussed from the numerical results. Next, this study investigates whether or not the natural frequency is accurate enough for practical usage by comparing the natural frequencies obtained numerically with those obtained experimentally. Finally, the effect of snow on the natural frequencies is discussed.  相似文献   

2.
A dynamic behaviour of thin periodic plates interacting with an elastic periodic foundation is analysed. The main aim is to investigate free vibrations and calculate frequencies for these plates. The presented modelling approach to the linear-elastic plates, having periodic structure in planes parallel to the midplane, is adopted from the tolerance averaging method developed by Woźniak and Wierzbicki (Averaging techniques in thermomechanics of Composite Solids, Wydawnictwo Politechniki Cz stochowskiej, Cz stochowa, 2000) for periodic composites. The obtained plate model describes the effect of the periodicity cell size on the overall plate behaviour. In this paper this effect is analysed in the free vibrations problem. Two special cases are taken into account: a square plate with a periodic thickness interacting with a homogeneous foundation and a square plate with a constant thickness interacting with a periodic foundation. A certain justification of the model is also presented.  相似文献   

3.
This paper intends to analyse free vibrations of beams in the geometrically non-linear regime and with plastic strains. The specific goal is to find how plastic strains combined with large displacements influence the non-linear modes of vibration, by analysing the influence of the former two factors in mode shapes and natural frequencies of vibration. The geometrical non-linearity is represented by the Von Kármán type strain-displacement relations. A stress-strain relation of the bilinear type, with isotropic strain hardening, is assumed, the Von Mises yield criterion is employed and the flow theory of plasticity applied. To obtain the time domain ordinary differential equations of motion the principle of virtual work is used and a Timoshenko p-version finite element model with hierarchical basis functions is adopted. The equations of motion are naturally different from the usual large displacement equations, due to the appearance of matrices and vectors related with plastic terms. In the cases studied, plastic strains are imposed on the beam by equally distributed static forces; the forces are then removed and a study on the free vibrations is carried out. It is assumed that, once defined, the plastic strain field does not change. The time domain equations are transformed to the frequency domain by the harmonic balance method and these frequency domain equations are solved by an arc-length continuation method. The variations of mode shapes of vibration and of natural frequencies with vibration amplitude are investigated. It is found that the plastic strain distribution defines if and how much softening spring effect occurs. Hardening spring effect always appears, but with some plastic strain fields hardening spring takes place only at large vibration amplitudes. Plastic deformations also have an important effect in the vibration shapes.  相似文献   

4.
The Finite Strip Method has been employed in the vibration problem of continuous rectangular plates on oblique supports. The structure has been divided into quadrilateral finite strips. The various properties of a quadrilateral finite strip have been derived using the displacement approach. The results are obtained for a two span rectangular plate with an oblique support at various angles and compared with other solutions. The results obtained due to various layouts of finite strips in the structure have been compared.  相似文献   

5.
Free vibration characteristics of a rotating pretwisted small aspect ratio blade, mounted on a disc at a stagger angle, are determined using classical bending theory of thin shells. Differential geometry of the blade in curvilinear coordinates are analysed and strain-displacement relations are established. The strain and kinetic energies of the rotating and vibrating blade are determined and the Lagrangian function is set up. Following the Ritz procedure, natural frequencies and mode shapes of the blade are determined. The results obtained from the present analysis compare well with some of the experimental and finite element results available in literature. Variation of natural frequencies with various parameters like pretwist, speed of rotation, stagger angle and disc radius is studied and the results are presented in a nondimensional form.  相似文献   

6.
In modern combat operations warships can be subjected to underwater blast loads capable of causing considerable structural damage. Research in the field of underwater explosion effects on structures has seen systematic developments since world war-I (WW-I) with the increased awareness that the possible underwater explosions and threats from the hunter killer “U” boats could now be countered. Most of the earlier investigations were conducted by military and these were classified. Cole [1] established empirical relations to model the underwater explosion (UNDEX) loading, which were the outcome of numerous experimental investigations done by the military agencies. In the present study the UNDEX load profile has been modeled as an exponentially decaying shock wave, which varies spatially and transiently. The failure modes in high strength (HS) and WELDOX Steel rectangular plates was predicted using an elasto-plastic model with isotropic hardening, strain rate effects and fracture criterion under clamped edge conditions. These models were implemented in the nonlinear finite element code ABAQUS/Explicit. The present study predicts and establishes the failure modes using a 3D FE analysis.  相似文献   

7.
Point connections representing spot welds, bolts, rivets, screws, pins, etc. have been included in the powerful panel analysis and design computer program VICONOPT. The exact stiffness matrices of component structures are coupled by using Lagrangian multipliers to represent these point connections between the structures. The new approach gives a very quick and accurate analysis when longitudinal lines of point connections are used in panels which are loaded only in compression. In this case only one point connection needs to be modelled and only certain response wavelengths contributing to the buckling mode are used. Accurate solutions are also obtained for shear loaded panels but at a much greater computational cost. Illustrative examples include comparisons between results for line and point connections, indicating to designers how many point connections are required to produce an effective line connection. These comparisons cover both pure axial compression and pure shear loading cases for both isotropic and anisotropic panels. They suggest that for many panels, manufacturing costs could be reduced by using fewer point connections, with minimal reduction in the stability of the panel. The work presented here is of particular importance to aircraft panels where point connections are extensively used to connect component structures together.  相似文献   

8.
The problem of flaw dimension measurement along the beam direction is discussed from the viewpoint of the measurement accuracy. Practical recommendation are put forth for estimating dimensions of flaws with small openings, such as incomplete fusions in welded joints, along the beam direction using X-ray photographs.  相似文献   

9.
The use of a pulsed variable-speed drive as a vibrational drive is studied theoretically and experimentally. The design of a transmission with controlled velocity fluctuation is considered.  相似文献   

10.
主要阐述了保持架座支柱伸出保持架盖部分的铆后的长度与高度对保持架性能的影响。运用SolidWorks有限元软件计算出在不同的支柱铆后长度、不同的支柱铆后高度时保持架的强度,最后根据不同情况下的对比结果选择合理的铆后长度和铆后高度,为保持架支柱的铆合参数提供一个理论依据。  相似文献   

11.
用ANSYS软件对机翼典型加筋整体壁板进行优化设计,并利用优化结果对加筋整体壁板进行稳定性分析和与原铆接壁板进行数值比较分析,该方法可为该类加筋板的设计提供参考.  相似文献   

12.
The vibrational behavior of cantilevers carrying externally mounted stores and featuring adaptive capabilities is investigated. The structure is modeled as a thin-walled beam, and the adaptive capabilities are provided by a system of piezoactuators bonded or embedded into the structure. Based on the converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied electric field and, as a result, an adaptive change in the dynamic response characteristics is achieved. Implementation of a control law relating the applied electrical field to one of the mechanical quantities characterizing the motion of the beam, enables one to obtain the free vibration characteristics as a function of the applied voltage (or in other terms, of the feedback gain).The obtained numerical results suggest that the application of this technology can play a major role in the enhancement of the dynamic response and the control of free vibration characteristics of this type of structures.  相似文献   

13.
The different types of the conditions of existence of the motion of two-mass nonlinear system are investigated. The system is made to vibrate by the pressure of opposite forces which—in dependence in the relative motion of the bodies—produce a hysteresis loop of the width 2h. One of the bodies may impact on a rigid stop which is placed at a distance r from the static position of the body. The regions of existence and stability of different types of self-excited vibrations with impacts in the plane (h × r) were found by modelling the system motion. The nature of the various boundaries of existence is explained with the aid of the amplitude characteristics of the relative motion of the bodies. A study is also made of the dependence of the impact velocity on the system's parameters, and the subregion in the (h × r) plane in which the impact velocities are maximum, is established.  相似文献   

14.
Journal of Mechanical Science and Technology - Cold-formed steel (CFS) sections are commonly applied to modern engineering structures, such as roof truss, purlin and industrial goods rack. This...  相似文献   

15.
Tripping of stiffeners is one of the buckling modes of stiffened panels which could rapidly lead to its catastrophic failure. Loss of thickness in the web and flange of stiffeners due to corrosion reduces elastic buckling strength. It is common practice to assume a uniform thickness reduction for corroded surfaces. To estimate the remaining strength of a corroded structure, a much higher level of accuracy is required since corroded surfaces are irregular. Finite element method is employed to analyze elastic tripping stress of corroded stiffeners with irregular surfaces. Comparing the results with elastic tripping stress of un-corroded stiffener, a reduction factor is introduced. It is found that for flat-bars and angle-bars the reduction factor increases by increasing corrosion loss; however, for tee-bars remains almost unchanged. Surface roughness has no significant effect on reduction of tripping Euler stress of angle-bars and flat-bars; however, it has an effect on reduction of tripping Euler stress of small flat-bars. For high values of corrosion loss, reduction of tripping Euler stress is higher in flat-bars than angle-bars. Corrosion at the mid-length or ends of flat-bars is more detrimental than full length. Corrosion at the ends of angle-bars is more detrimental than full length and mid-length.  相似文献   

16.
The helium-air exchange flow may occur at the rupture accident of a standpipe in a high temperature engineering test reactor. A test vessel with three types of small opening is used for experiments. An estimation method of mass increment is applied to measure the exchange flow rate. Flow measurements are made with the single opening and partitioned, opening, for opening ratiosH 1/D 1 in the range 0.05 to 10, whereH 1 andD 1 are height and diameter of the opening, respectively. At lower opening ratios (H 1/D 1<0.75), the difference in the exchange flow rates between the opening systems is small. At higher opening ratios (H 1/D 1≥0.75), exchange flow rates of the partitioned opening system are higher than those of the single opening system because of separated (unidirectional) flows by partition. An effect of variation of diameters of the partitioned openings on the exchange flow rate is investigated. The exchange flow rate increases with the opening diameter. Finally, an experiment with two-opening is designed to investigate the effect of fluid interaction of the partitioned opening system. It is demonstrated that the exchange flow rate of the two-opening system is higher than that of the partitioned opening system because of the absence of the fluid interaction.  相似文献   

17.
The problem of the motion of an imbalanced rotor when passing through a resonance zone is solved by the iteration method combined with the method of the direct separation of motions.  相似文献   

18.
A method for calculating the residual strength of a stiffened structure (panel) taking into account the stable growth of a crack is presented. The use of the R curve of material is based on experimental data. Calculated results are compared with experimental data.  相似文献   

19.
Investigations of the direct and inverse spectral problems of torsional vibrations of a shaft with disks were performed. The Tolle method was used to solve the direct problem. The influence of the characteristics of a shaft with loads on the frequencies of its torsional vibrations was studied using the solution of the direct problem. It was shown that an increase in the moments of inertia of disk masses leads to a decrease in vibration frequencies and that an increase in the torsional rigidity of segments of a shaft leads to an increase in the system’s vibration frequencies. Examples, tables, and plots of the corresponding dependences are presented.  相似文献   

20.
An optimization design method is presented to reduce the undesirable vibrations caused by clearance for planar linkage mechanism. A clearance joint is defined and considered a contact/impact force constraint. Contact and impact force models for the clearance joint are established using a normal contact force model based on Hertz model with energy loss and a tangential friction model based on modified Coulomb model with dynamic friction coefficient, respectively. In view of the clearance joint, dynamic equations and optimization method for a planar four-bar mechanism are then presented as an application example. The optimization aims to minimize the maximum absolute acceleration peaks of the mechanism by determining the link lengths of the planar linkage mechanism. Finally, the optimization design is solved by a generalized reduced gradient algorithm. Results show evident decrease in vibration peaks of the mechanism and obvious reduction in the contact forces in the clearance joint, which contribute to a good performance of planar linkage mechanism systems.  相似文献   

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